The invention concerns a system for applying one or more coats to the top and/or bottom of strips of backing and for manufacturing strip without any backing with, or from, one or more such materials as asphalt, possibly sprinkled with such a material as granulated slate, silica sand, talc, etc. and optionally covered with sheeting or a similar material.
Strips of coated backing are needed in a very wide range of technical applications. There is an urgent demand for example for strips of roofing material coated with asphalt, and a version that is substantially easier to apply because it has a layer of adhesive activated just before the strips are laid is being used more and more often. Since neither their plastic base nor their asphalt coat is resistant to ultraviolet light, the asphalt on the upper surface of these strips is sprinkled with such a material as granulated slate to protect it from the sun. In addition to roofing, there are many other applications for coated material--as insulation for buildings and vehicle bodies for example.
Coating such strips while they are still raw or once they have been impregnated by soaking in dilute asphalt an while they are spread out horizontal (or formerly suspended vertical) is known. Asphalt is applied to the base in excess either from below with a roller or from above and below by immersion and then stripped off to the desired thickness with two calibrating rollers. Systems in which appropriate volumes of asphalt are introduced from above and applied to the top of the base are also known. The excess escapes into a heated trough. The base is drawn along horizontally while a roller scoops asphalt onto it from below. The excess asphalt flows over an adjustable-height weir and is pumped back into an associated agitator. Since known devices employ large pans with a capacity of approximately 1000 1, a lot of material is lost when it is replaced with a different material, and a lot of energy is consumed in heating the pan. Large pumps are needed to recirculate the excess, which is of course also considerable.
Another drawback of the known systems and device is that, since the intermediate layer cannot be precisely controlled, the amount of asphalt to be applied to the upper and lower surface cannot be precisely dictated. It is impossible to measure the product, to determine the thickness of the final product, that is, immediately after coating because it is not supported in that vicinity but hangs free. The base "floats" to a certain extent between the top and bottom coats, and it is impossible to precisely define the distance up and down. The lack of support, especially once the particles have been sprinkled onto the upper surface, results in severe sagging that generates substantial stress that in turn leads to shrinkage, especially of thermoplastic bases. Since it is impossible to measure how thick the product is immediately after the coats have been applied to the base, it will be just as impossible to carry out any corrections at that point, and the quality of the product suffers. Raw materials are lost. Too thick a coat entails a loss to the manufacturer and too thin a coat results in rejection.
The product can admittedly be provided with better surface properties in known drawing devices, although the aforesaid drawbacks are still present. Another drawback of the known device is that substantial blistering always occurs when sheet is bonded to the upper or lower surface because the sheet bonds immediately and uncontrolled, capturing air that produces the blisters. The sheet must be relatively thick in that the coatings are modified and include fillers, so that they must be processed at approximately 160.degree. to 180.degree. C., temperatures at which a thin sheet would melt very rapidly. The result is malfunctions due to the hot asphalt clogging up the conventional machinery. Again, multiple coating in particular is difficult and poorly controlled because it requires a series of the aforesaid large pans. The asphalt must be applied to the upper surface of the base in a considerable excess in known systems. Some of the surface of the asphalt will accordingly cool, leading to areas of different temperature inside the laminator that have a negative effect on the coat's uniformity. Surface properties sometimes suffer, and the extent that the sprinkling material adheres to will vary, causing streaks. Again, the rollers will pick up the hot asphalt after the calibration process, independently from the aspect of fluid mechanics of whether they are stationary or rotating in opposite senses, which can again apply stress to the base. The excess sprinkling material is recycled in known systems by vibrating conveyors and screws or belts that convey it to the side and by elevators that raise it and return it to its hopper. These mechanisms involve considerable engineering expenditure and take up a lot of space. Since the sprinkling material ls very abrasive, the components that handle it wear out rapidly. The known systems accordingly have substantial drawbacks that impede the manufacture and coating of high-quality strip bases.
Furthermore, since the known systems are very complicated to operate, the quality of the products extensively depends on the skill and knowledge of the particular operators. The manufacturing range of the state-of-the-art systems is also very restricted. The limitations of the current methods appear very rapidly when heat-unstable base materials are employed.
Typical of another known system is that the surface remains too tacky the asphalt adheres to the rollers. Although the sheet must travel along in this system, it represents nothing but waste. At lower temperatures the coat exerts powerful stresses, which leads again to poor surfaces. The surface is sprinkled with sand, and the excess is not removed.